1. Description of the Invention
The invention relates to an endoscope having a generally elongated flexible shaft extending therebetween a control head and an objective assembly and more particularly relates to a flexible endoscope having a cable compensating mechanism for protecting an operating cable and sheath assembly against excessive tensile forces when the objective assembly at the distal end of the endoscope is restrained. The endoscope of the present invention also includes a ratchet control mechanism to inhibit reversal of motion during adjustment of the objective assembly.
2. Description of the Prior Art
Endoscopes are well-known in the art. Typically, endoscopes are optical imaging devices used for viewing objects within cavities or the internal surface of cavities. Certain endoscopes have working channels for insertion of devices to act upon or treat conditions within an operative site.
While the herein described invention has application in many fields, it has particular relevance to the medical field wherein flexible endoscopes are employed to view and treat deep and convoluted passages of the human body.
Endoscopes are also used with ultrasonic transducers mounted at the distal end. Such endoscopes are inserted through the esophagus and into the fundus of the stomach. The distal end of the endoscope is then scanned to generate an ultrasonic image of an area, such as, for example, the heart. This procedure is generally referred to as Transesophageal Electrocardiogram ("TEE").
In a typical endoscope designed for such purposes, the distal tip of the instrument is made maneuverable by employing two or more angularly spaced cables which interact mechanically with a series of vertebrated or specifically profiled rings located adjacent to the distal end of the instrument. Bending and deflection of the rings is obtained by tensioning and relaxing the cables by actuating the controls located at the proximal end of the endoscope on the control head. The means for applying tension and relaxing forces to these cables have been the subject of extensive technological effort resulting in controls such as joysticks or coaxial control wheels found on many well-known endoscopes. The object of these efforts has been to provide on the control head of the endoscope cable tensioning and relaxing means accessible and comfortable to the hands and fingers of the operator, and, consistent with holding the scope, operating all other controls, and allowing such other manipulations of the endoscope (i.e., torque, pushing and pulling) as are deemed effective for the clinical procedure for which the endoscope was designed.
One such cable compensation mechanism is disclosed in U.S. Pat. No. 4,688,555. The compensation mechanism engages the cables intermediate their ends and is effective to guard the cable against excessive loads and also to readily accommodate variations in the working length of the cables as occurs when the cable are permanently stretched.
Throughout this disclosure, it will be appreciated that the term "cable" is intended to refer to any elongate material which can be effectively utilized to operatively connect the distal end of the instrument to the control head. Thus, for purposes of the invention, wire, bands, chains and the like are considered to be equivalent to cables. The term "operating cable and sheath assembly" refers to an assembly comprising a cable located with a sheath wherein the cable moves within the sheath.
In the practice of medicine, a common form of such a device is used for inspection of the human ureter while a similarly structured device is used for inspection of the urethra and bladder. The endoscope is conventionally used in the diagnosis of tumors and other conditions in the urinary tract. The endoscopic examination involves the physician observing the urinary or vesical wall through an eyepiece in the control head of the instrument. Generally, the endoscope is provided with a source of illumination at its objective end, the end which is placed adjacent the area to be examined, and a bundle of light-transmitting fibers through which an image of the examined area is transmitted back to the eyepiece. The endoscope can further incorporate a channel which provides a washing fluid for application to the site under examination as well as a surgical tip and other features.
In TEE procedures, the distal tip of the endoscope could become internally restrained by contacting tissue or bone within the cavity during the procedure. In such event, the cable could be subject to a high tensile force or could break. If the distal tip is in a curved or deflected position and mechanically becomes fixed in the deflected position, it becomes difficult to remove the endoscope from a patient.
A factor to be considered in the construction of the endoscope for its normal medical use is its flexibility and articulation which permits the objective tip to be directed along a selected passageway such as in the esophagus or in the urinary tract. An endoscope can be made to traverse a considerable distance within the selected passageway providing that any bends in the channel have a sufficiently large radius of curvature to enable the objective assembly of the endoscope to be readily articulated to follow the course of the passageway. Care must be taken, however, to precisely guide the instrument so as not to puncture any cavity or passageway walls such as the vesical wall, especially as the device is being inserted.
Endoscopes are also used for inspecting mechanical structures requiring elongated tubular inspection devices. Typically, such endoscopes incorporate flexible fiber optics. One application is to inspect the first stage or high temperature stage of a jet engine just behind the burner in that such components are most subject to wear and deterioration. The arrangement of the jet engine's rotor and stater blades, particularly those in the high temperature state of the engine, presents a most complex geometry which has not been amenable to inspection in the past other than by first disassembling the engine.
While the state-of-the-art relating to endoscopes is relatively advanced today, there are still recurring problems which result when excessive stresses are applied to the operating cables by the hand operated control mechanism. In an extreme situations, this can result in breakage of the cable or, in a less extreme situation, to permanently stretching of the cable. In the former instance, the endoscope is rendered useless until the cable has been replaced. In a latter instance, the endoscope loses a portion of its original deflection capability, making it necessary to take up the slack of the stretched cable and to recalibrate the instrument. In both instances, it is necessary to repair the instrument to its former operating condition. This procedure, of course, results in considerable downtime thereby creating scheduling problems, possibly delaying for long periods of time critical inspection procedures which cannot be performed until the instrument has been repaired.